Interactive (smaller) groups activity needed in 2nd half of workshop

[libcce]

The group exercise(s) in processing a data file worked well before heading off to lunch/a break; however, since the attendees are staring at a screen for hours, it would be nice to have an interactive groups excercise that didn't involve their screens (involved post its, paper, anything beyond their computers). Overload can be a factor later in the day and attendees need a break/need to think about programming via another, interactive mode with other attendees.